Eeek! Nosema in my bees! – The Complete Guide (2022)

I thought I would just look around a little for Nosema in my bees.

So my first disclaimer is that I am NOT a Nosema or honeybee expert! I’m a first-year beekeeper, but I’ll chat about what I found in my bees and some things I learned in a recent intermediate beekeeping course I took.  

honey comb

The classes were offered by one of our local beekeeping clubs and one night the beekeeper who was teaching spoke about Nosema in bees. I thought, “I can use the microscope at work and look around in my bees for some Nosema,” thinking I wouldn’t find any. So I scooped some bees out of the snow and picked 5 to look at and saw HUNDREDS of Nosema spores under the microscope:

Then I picked 5 bees each from INSIDE hives A and C and looked at them separately: nothing. (I didn’t sample from hive B because I tacked the tar paper up too high and can’t get into it easily – doh!

Could all the Nosema I saw the first time have been from hive B? I was convinced by my hubby while he was snowshoeing, to stop and collect dead bees from in front of the hives into 3 plastic bags. I again sampled 5 bees each time and under the microscope, I found a few Nosema from hive A bees and none from hive B or hive C.

I really thought I would find more Nosema in hive B because it’s the smallest hive, the one that’s failing to thrive and the most likely to freeze due to the small population before Spring. But reading more about Nosema, they recommend sampling 30-60 bees in the hemocytometer protocol from the University of Minnesota.

Randy Oliver recommends on his website, sampling 30-50 bees. I think they’re right. I think I could have just gotten a one really sick bee in my first sample and because 1 sick bee can have up to 30 million spores in its gut, I thought all the bees were really sick. So, lesson learned: I need to sample about 50 bees each time. (Although I read that can be difficult in warm weather because the best bees to sample are returning foragers.)

What I learned about Nosema

Nosema is a disease of honeybees, caused by microsporidia which have been recently reclassified as fungi. Bees ingest Nosema spores when eating or drinking. The spores then germinate and multiply in a layer of the midgut of bees. The bees excrete the spores in their feces. The spores can remain viable for up to one year in fecal material and the cycle continues.

There are two species of Nosema. There’s Nosema apis which has been in the US since our grandparents’ time and can cause some dysentery or diarrhea in the bees. A more recent introduction from the Asian honey bee is Nosema cerenae, which is much more serious and seems to be replacing the more mild N. apis.

It’s very likely that I saw Nosema ceranae in my bees, although they can be very difficult to tell apart.

Nosema apis

  • causes diarrhea

If you don’t have bees yet or haven’t seen bee poop yet, this is what it looks like:

When we open a beehive, we shouldn’t see bee poop inside the hive. Nor should we see it streaking down the front of the hive. That indicates our bees have N. apis, maybe N. ceranae, or dysentery from something else.

Nosema ceranae or “dry Nosema”

This is much more serious than the N. apis our grandparents dealt with and has vague symptoms.  It can kill a hive in 8 days. It can be confused with:

  1. other diseases
  2. pesticide poisoning
  3. mite predation

Symptoms include:

  • increased winter losses
  • decreased honey production
  • colonies fail to thrive
  • the queen lays fewer eggs if she’s sick – decreased brood production
  • workers can’t feed the brood as well with their GI tract affected by the disease – decreased brood
  • the hive will supersede the queen (“supersedure”: the worker bees decide something is wrong with the queen, kill her and raise a new queen)
  • foragers often die when out in the field
  • bees unable to fly or only flying short distances
  • bees trembling or quivering
  • dysentery/diarrhea
  • bees crawling aimlessly  outside hive on landing board
  • bees dragging themselves like their legs are paralyzed
  • K wing (see pic below)
  • abdominal distension
  • won’t take/eat sugar syrup
  • workers may abandon the colony leaving the queen and emerging workers behind

Diagnosing Nosema

  • you can dissect a bee and evaluate its hindgut – picture in PennState/MAAREC’s “A Field Guide to Honey Bees and Their Maladies,” see bottoms of pp 44 and 45
  • you can collect bees, cut off their abdomens & masticate them in water then evaluate the fluid for spores – Marla Spivak’s Univ Minnesota’s Bee Lab & Randy Oliver’s Scientific Beekeeping for protocols
  • you can send bees to the Beltsville, Maryland USDA lab (although I’ll give you a heads up that they won’t tell you if you have N. apis or N. cerana), but another beekeeper I’m friends with on Instagram mentioned that at the Penn State Beekeeping Seminar with the Bee Informed Partnership and the U of Maryland, they claimed N. apis to be almost non-existent in their testing.

Treating Nosema

  • fumagillin – an anti-fungal available in the US. Difficult to get bees to take it in syrup when they’re sick, can use a drench technique, not very effective, expensive, resistance may develop, there may be a researcher is concerned it may become a human pathogen (if I understood my beekeeping teacher correctly?!)
  • transplant colony into an uncontaminated hive, add fresh brood from a healthy hive, remove all comb that still has spores
  • heat hive components: up to 120ºF for 24 hours, making sure there’s no honey or pollen in the comb (over 120ºF and wax melts)
  • 10% bleach all woodenware
  • fumigation chambers using acetic acid – some states have
  • take gear to irradiation facility for gamma radiation treatment – some states have
  • use individual waterers if a small apiary – can use Boardman feeders
  • keep ventilation good in winter and an upper entrance open for cleansing flights
  • keep hives in sun in summer
  • make sure the hive has good nutrition
  • reduce stress, minimize moving hives
  • don’t combine failing hives with strong hives
  • keep only clean combs – sterilize or destroy combs with fecal material on them

Read and listen to others!!!

Remember, I’m just a noob, so do your due diligence if you think your bees have Nosema. Go to beekeeping meetings, talk to experienced beekeepers, poke around reliable sites on the interwebz, take classes, and attend seminars. There’s always more to learn!

Comment below

If you are an experienced beekeeper and have experience with Nosema or good resources to point us noobs to, please add them below. Fellow noobs, please comment with your thoughts and experiences. I welcome input from folks!